Multiple Choice Questions (MCQ) - Power Systems

Power Systems Objectives:


1. The surge impedance of 50 miles long underground cable is 50 ohms. For a 25 miles length it     will be:
    (a) 25 ohms        (b) 50 ohms     (c) 100 ohms           (d) None of the above

    Answer: b
    Hint: Surge impedance does not change with the length.

2. For a load floe solution the quantities normally specified at a voltage controlled bus are:
    (a) P and Q     (b) P and |V|     (c) Q and |V|     (d) P and delta.

   Answer: b
   Hint:     Load bus :  P and Q
             Generator (or) voltage controlled bus : P and |V|
             Slack bus : |V| and delta.

3. For reducing tower footing resistance it is better to use:
   (a) Chemical and ground rods only.
   (b) Chemical and counterpoise only.
   (c) Ground rod and counterpoise only.
   (d) Chemical, ground rods and counterpoise.

    Answer: c

4. The positive, negative and zero sequence impedance of a solidly grounded system under             steady condition always follow the relations:
   (a) Z1 > Z2 >  Z0                                                       (b) Z1<  Z2 < Z3
   (c) Z0 > Z1 > Z2                                                        (d) None of the above.

   Answer: a

5. Mho relay is normally used for the protection of:
   (a) Long transmission lines                    (b) Medium transmission line
   (c) Short transmission line                     (d) No length criterion.

   Answer: a
   
    Hint:
                       R - Reactance relay  :  Short transmission line.
                       I  - Impedance relay :  Medium transmission line.
                       M - Mho relay         :  Long transmission line.

6. Reactance relay is normally preferred for protection against:
   (a) Earth faults only                 (b) Phase faults only
   (c) None of the above.

Anawer: a

7. If the  fault current is 2000 amps, the relay setting 50% and the C,T, ratio is 400/5, then the plug setting multiplier will be:
    (a) 25 amps              (b) 15 amps      (c) 50 amps   (d) None of the above.

Answer: d                    

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